Adherence to intermittent preventive treatment for malaria in Papua New Guinean infants: A pharmacological study alongside the randomized controlled trial

Background

The intermittent preventive treatment in infants (IPTi) trial that took place in Papua New Guinea showed an overall reduction of 29% of the risk of malaria when delivering single-dose sulfadoxine-pyrimethamine (SP) associated to 3 days of amodiaquine (AQ) every three months to children during the first year of life. The aim of the present study was to assess if the last two doses of AQ were truly administered as prescribed by the parents at home based on drug level measurement and PK modelling, which is a good proxy of medication adherence. It provides also important information to discuss the efficacy of the intervention and on feasibility of self-administered preventive malaria treatment.

Methods and findings

During the three-arm randomized double-blinded IPTi trial, each child was prescribed one dose of SP (day 0) and 3 doses of either AQ or artesunate (AS) at day 0, 1 & 2 adjusted to weight or placebo. Treatments were given at 3, 6, 9 and 12 months of age. The first day of treatment was delivered by nursing staff (initiation under directly observed treatment (DOT)) and the two last doses of AQ or AS by parents at home without supervision. For this cross-sectional study, 206 consecutive children already involved in the IPTi trial were enrolled over a 2-month period. At the time of the survey, allocation of the children to one of the three arms was not known. Blood samples for drug level measurement were collected from finger pricks one day after the planned last third dose intake. Only children allocated to the SP-AQ arm were included in the present analysis. Indeed, the half-life of AS is too short to assess if drugs were given on not. Because of the short half-life of AQ, desethyl-AQ (metabolite of AQ (DAQ)) measurements were used to investigate AQ medication adherence. Two PK (PK) models from previously published studies in paediatric populations were applied to the dataset using non-linear mixed effect modelling (NONMEM) to estimate the number of doses really given by the parents. The study nurse reported the administration time for the first AQ dose while it was estimated by the parents for the remaining two doses. Out of 206 children, 64 were in the SP-AQ arm. The adjusted dosing history for each individual was identified as the one with the lowest difference between observed and individual predicted concentrations estimated by the two PK models for all the possible adherence schemes. The median (range) blood concentration AQ in AQ arm was 9.3 ng/mL (0–1427.8 ng/mL), (Quartiles 1–3: 2.4 ng/mL -22.2 ng/mL). The median (range) for DAQ was 162.0 ng/mL (0–712 ng/mL), (Quartiles 1–3: 80.4 ng/mL-267.7 ng/mL). Under the assumption of full adherence for all participants, a marked underprediction of concentrations was observed using both PK models. Our results suggest that only 39–50% of children received the three scheduled doses of AQ as prescribed, 33–37% two doses and 17–24% received only the first dose administered by the study nurse. Both models were highly congruent to classify adherence patterns.

Conclusions

Considering the IPTi intervention, our results seem to indicate that medication adherence is low in the ideal trial research setting and is likely to be even lower if given in day-to-day practice, questioning the real impact that this intervention might have. More generally, the estimation of the number of doses truly administered, a proxy measure of adherence and an assessment of the feasibility of the mode of administration, should be more thoroughly studied when discussing the efficacy of the interventions in trials investigating self-administered malaria preventive treatments.

Practical HPLC methods for the quantitative determination of common antimalarials in Africa

This article describes high-performance liquid chromatographic assays for the quantification of sulfadoxine (SDX), pyrimethamine (PYM), chloroquine (CQ), amodiaquine (AQ) and desethylamodiaquine (AQM) from whole blood. All four assays were set up and validated in Malawi using a common high-performance liquid chromatography platform and column and involved the use of simple mobile phase and extraction reagents. Calibration curves were linear (r(2)>0.95) in the ranges 5-100microg/ml, 50-1000, 150-1500, 100-1000 and 100-1000ng/ml for SDX, PYM, CQ, AQ and AQM, respectively. Intra-assay and inter-assay coefficients of variation were <15% at 3 points spanning the concentration range and <20% at the lower limit of quantification. The assays were specific with no interference from the other antimalarials described in this report. All four assays use liquid-liquid extraction, reversed-phase chromatography and UV detection and require between 50 and 200microl of blood. Because the assays share common instruments and reagents, they are cost-efficient and could be used to optimise antimalarial drug therapies in other resource poor settings.

Markers of sulfadoxine-pyrimethamine-resistant Plasmodium falciparum in placenta and circulation of pregnant women

Placental sequestration of Plasmodium falciparum in pregnancy may impair the usefulness of molecular markers of sulfadoxine-pyrimethamine resistance. In 300 infected, delivering women, the concordance of PCR-restriction fragment length polymorphism-derived parasite resistance alleles in matched samples from placenta and circulation was 83 to 98%. Sulfadoxine-pyrimethamine resistance typing in peripheral blood is reasonably representative of P. falciparum infecting pregnant women.

Efficacy of sulfadoxine-pyrimethamine in the treatment of uncomplicated Plasmodium falciparum malaria in East Timor

The efficacy of sulfadoxine-pyrimethamine (SP) in East Timor is unknown. We treated 38 individuals with uncomplicated Plasmodium falciparum malaria with SP and monitored the outcome for 28 days. Recrudescent parasitemia, confirmed by genotyping, were detected in three individuals resulting in a late treatment failure rate of 7.9% (95% confidence interval = 1.7-21.4%). The results suggest that SP is still efficacious in treating uncomplicated P. falciparum malaria in East Timor. However, the useful life of SP in East Timor may be limited because 80% of the parasites in our samples were found to already carry double mutations in P. falciparum dihydrofolate reductase (S108N/C59R). The data from this study also highlights that the presence of gametocytes may significantly influence the estimate of SP efficacy determined by genotyping.

Adoption of the new antimalarial drug policy in Tanzania - a cross-sectional study in the community

OBJECTIVE

To assess the diffusion of the change of first line antimalarial drug from chloroquine (CQ) to sulphadoxine/pyrimethamine (SP) at household level in a rural district of Tanzania less than a year after the policy implementation.

METHODS

Caretakers in 729 households were interviewed on knowledge of the new policy, home stocking of antimalarials, home-treatment practices of children younger than 5 years with fever, health-seeking behaviour and experience of SP. SP and CQ levels in blood were analysed from 328 children younger than 5 years in the households. Twelve focus group discussions (FGD) were performed with mothers, fathers and health workers.

RESULTS

About 51% of the population knew that SP was the first line antimalarial. Only 8% of mothers stocked antimalarials, and only 4% stated self-treatment as the first action. We estimated that 84% of the children who had had fever during the last 4 weeks sought care at public health facilities. SP was detectable in 18% of the total child population and in 32% of those with reported fever, CQ in only 5% and 7%, respectively. The FGDs revealed negative perceptions of SP and fear of severe adverse reactions with mass media reported as key informant.

CONCLUSION

The policy had diffused to the communities in the sense that CQ had been changed to SP, which was well known as first line treatment. Moreover, there was a reported dramatic change from self-treatment with CQ to seeking care at public health facilities where SP was given under observation.

Concentraciones sanguíneas de sulfadoxina y pirimetamina según la respuesta terapéutica antimalárica, en dos municipios de Antioquia, Colombia

PROBLEM

There has been a constant increase in the level of therapeutic failure of the sulfadoxine-pyrimethamine (SP) combination for treating uncomplicated Plasmodium falciparum malaria.

OBJECTIVE

To use high-performance liquid chromatography to quantify blood levels of SP in patients with good clinical response and in patients who did not respond to treatment.

METHODS

This experimental study was carried out in 2002 in Turbo and Zaragoza, two municipalities in the department of Antioquia in Colombia. There were 79 patients (45 in Turbo and 34 in Zaragoza), including both men and women, who ranged in age from 1 year to 60 years. All the patients had uncomplicated Plasmodium falciparum malaria, with a parasite density of 500 to 50,000 parasites/microL. The patients were each randomly assigned to a treatment group. The treatment groups were not blinded; the physician who provided the medication also evaluated the therapeutic response. The treatment consisted of a single combination dose of sulfadoxine (25 mg/kg) and pyrimethamine (1.25 mg/kg) in tablets (500 mg of sulfadoxine and 25 mg of pyrimethamine). Clinical-parasitological follow-up was carried out for 21 days. Blood levels of sulfadoxine and pyrimethamine were measured two hours after the treatment was given and also the day of treatment failure, if that occurred.

RESULTS

Two hours after the treatment was given, the median blood level of sulfadoxine was 136.6 micromol/L in the patients who later showed a good clinical response, and it was 103.4 micromol/L among those who did not respond to treatment (P = 0.13). The medians for pyrimethamine were 848.4 nmol/L in patients with a good clinical response and 786.1 nmol/L in patients with treatment failure (P = 0.40). There were no significant differences in drug levels between the early-failure cases and the late-failure cases. The linear correlation between the blood levels of sulfadoxine and pyrimethamine was close to zero (r = 0.13).

CONCLUSIONS

Between 1998 and 2002, treatment failure with the SP combination increased from 13% to 22% in Turbo, and from 9% to 26% in Zaragoza. The lack of response in 2002 could not be explained by lower blood levels of the medications.

Liquid chromatographic–mass spectrometric assay for simultaneous pyrimethamine and sulfadoxine determination in human plasma samples

We present a liquid chromatographic-mass spectrometric assay for the simultaneous determination of sulfadoxine and pyrimethamine in human plasma samples. Sample clean-up was achieved by adding acetonitrile for protein precipitation. Gradient elution in only 10 min resulted in high throughput capability. Tandem mass spectrometric detection in multiple reaction monitoring was used for quantification. The developed analytical approach was successfully validated and was applied in the pharmacokinetic evaluation of the bioavailability between two sulfadoxine/pyrimethamine formulations available on the Eastern African market, using a cross-over design.

Multi-drug resistant Plasmodium falciparum malaria in Assam, India: timing of recurrence and anti-malarial drug concentrations in whole blood

The susceptibility of 23 cases of Plasmodium falciparum malaria from the Sonapur primary health center in the Kamrup district of Assam, India to different antimalarials was investigated using the 28-day World Health Organization in vivo test. Whole blood concentrations of chloroquine, sulfadoxine, and quinine were determined at different intervals and at the time of parasites recrudescence after completion of treatment with the respective drugs to confirm the status of drug sensitivity. A case of multi-drug resistant P. falciparum malaria was found where recrudescence occurred, despite standard oral treatment with chloroquine, sulfadoxine/pyrimethamine, and quinine sequentially. Whole blood concentrations of chloroquine, sulfadoxine, and quinine at the time of recrudescence were 0.35 microg/ml (day 7), 18 microg/ml (day 14), and 0.009 microg/ml (day 14), respectively. Therefore, monitoring of drug-resistant P. falciparum malaria and its proper treatment should be intensified to check the spread of multi-drug resistant strains in other parts of the country.

Combination of drug level measurement and parasite genotyping data for improved assessment of amodiaquine and sulfadoxine-pyrimethamine efficacies in treating Plasmodium falciparum malaria in Gabonese children

Many African countries currently use a sulfadoxine-pyrimethamine combination (SP) or amodiaquine (AQ) to treat uncomplicated Plasmodium falciparum malaria. Both drugs represent the last inexpensive alternatives to chloroquine. However, resistant P. falciparum populations are largely reported in Africa, and it is compulsory to know the present situation of resistance. The in vivo World Health Organization standard 28-day test was used to assess the efficacy of AQ and SP to treat uncomplicated falciparum malaria in Gabonese children under 10 years of age. To document treatment failures, molecular genotyping to distinguish therapeutic failures from reinfections and drug dosages were undertaken. A total of 118 and 114 children were given AQ or SP, respectively, and were monitored. SP was more effective than AQ, with 14.0 and 34.7% of therapeutic failures, respectively. Three days after initiation of treatment, the mean level of monodesethylamodiaquine (MdAQ) in plasma was 149 ng/ml in children treated with amodiaquine. In those treated with SP, mean levels of sulfadoxine and pyrimethamine in plasma were 100 microg/ml and 212 ng/ml, respectively. Levels of the three drugs were higher in patients successfully treated with AQ (MdAQ plasma levels) or SP (sulfadoxine and pyrimethamine plasma levels). Blood concentration higher than breakpoints of 135 ng/ml for MdAQ, 100 micro g/ml for sulfadoxine, and 175 ng/ml for pyrimethamine were associated with treatment success (odds ratio: 4.5, 9.8, and 11.8, respectively; all P values were <0.009). Genotyping of merozoite surface proteins 1 and 2 demonstrated a mean of 4.0 genotypes per person before treatment. At reappearance of parasitemia, both recrudescent parasites (represented by common bands in both samples) and newly inoculated parasites (represented by bands that were absent before treatment) were present in the blood of most (51.1%) children. Only 3 (6.4%) therapeutic failures were the result not of treatment inefficacy but of new infection. In areas where levels of drug resistance and complexity of infections are high, drug dosage and parasite genotyping may be of limited interest in improving the precision of drug efficacy measurement. Their use should be weighted according to logistical constraints.

Efficacy of trimethoprim-sulfadoxine against Escherichia coli in a tissue cage model in calves

Tissue cages implanted subcutaneously in calves were infected with Escherichia coli. Twenty-four hours later, the calves were treated either with single doses of 2.5 + 12.5 or 5 + 25 mg/kg trimethoprim (TMP) + sulfadoxine (SDX) or with five doses of 7.5 + 37.5 mg/kg TMP + SDX at 12-h intervals. In addition, one cage in each of three calves in the highest dose group was infected 3 h after initiation of treatment. Untreated calves were kept as controls. Concentrations of TMP and SDX in plasma and tissue cage fluid (TCF) and counts of viable bacteria in TCF were determined. In the highest dose group, concentrations of TMP in TCF remained above the minimum inhibitory concentration of the test strain for 94-101 h and peak to minimum inhibitory concentration (MIC) ratio was close to 10. In spite of this, an effect of treatment was noted only in cages infected after initiation of treatment. In vitro studies and analysis of thymidine content in serum and TCF from calves suggest that levels of thymidine in TCF are high enough to antagonize the antibacterial effect of TMP. The results indicate that soft tissue infections in secluded infection sites of calves are refractory to treatment with TMP + SDX.

Pyrimethamine/sulfadoxine combination in the treatment of uncomplicated falciparum malaria: relation between dihydropteroate synthase/dihydrofolate reductase genotypes, sulfadoxine plasma levels, and treatment outcome

Several in vitro studies have shown the correlation between mutations in dhfr and dhps genes and resistance to pyrimethamine/sulfadoxine (PYR/SDX) combination, but the in vivo correlates of these mutations with PYR/ SDX efficacy have not been investigated fully. We assessed PYR/SDX efficacy in relation to the frequency of dhfr and dhps mutations in 37 Plasmodium falciparum isolates sampled before treatment. Plasma levels of SDX measured at days 0, 3, 7, and 14 ascertained drug absorption. Point mutations were detected only at codons 51 and 108 of dhfr and codon 436 of dhps. The frequency of dhfr 51/108 and dhps 436 mutations was 79% and 8%. The plasma levels of SDX indicated adequate drug absorption by all patients. The presence of Ile 51 and Asn 108 mutations among parasites that cleared after treatment indicates that these mutations alone are insufficient to cause in vivo resistance. In all recrudescent parasites, however, the presence of Ile 51/Asn 108 dhfr mutations was coupled with the dhps Ala 436. The findings suggest that the presence of Ile 51/Asn 108 dhfr mutations and Ala 436 dhps confers decreased susceptibility of P. falciparum to PYR/SDX in areas of low endemicity.

High-performance liquid chromatographic assay for the simultaneous determination of sulfadoxine and pyrimethamine from whole blood dried onto filter paper

A method using solid-phase extraction and high-performance liquid chromatography is evaluated for the simultaneous determination of sulfadoxine and pyrimethamine from 0.1 ml of whole blood dried onto filter paper. Extraction recoveries are about 60% for both drugs. The coefficient of variation for intra-assay precision, inter-assay precision and accuracy is less than 10% for sulfadoxine (10-100 microg/ml) and pyrimethamine (1-10 microg/ml).

Determination of sulfadoxine in human blood plasma using packed-column supercritical fluid chromatography

A sensitive, rapid, selective and reproducible method has been developed to measure plasma levels of sulfadoxine, 4-Amino-N-(5, 6-dimethoxy-4-pyrimidinyl) benzensulfonamide; in healthy, human volunteers using packed-column super-critical fluid chromatography. Omeprazole, 5-methoxy-2-[[(4-methoxy-3, 5-di-methyl-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole; was used as the internal standard (i.s.) at 15.0 microg/ml. The drug and the i.s. were extracted from plasma using dichloromethane. Separation of sulfadoxine and i.s. was done on a Nucleosil (250x4.6 mm) 10 microm, RP-C18 column with 7.4% (v/v) methanol-modified supercritical fluid carbon dioxide (2.5 ml/min) as the mobile phase. The column temperature was 40 degrees C and the outlet pressure was set at 8.83 MPa. The detection was done using a UV-Vis detector set at 265 nm. The limit of quantification was 0.50 microg/ml using 1 ml plasma specimen. The mean extraction recovery of the drug from plasma was found to be 94.9%. The SFC method was directly compared to a published HPLC/UV method. With respect to speed and use of organic solvents SFC was found to be superior; while in all other aspects the results were similar to the published technique. The method has been successfully used to estimate the sulfadoxine levels in healthy human volunteers from 0 to 240 h following an oral dose of 500 mg of sulfadoxine in combination with 25 mg of pyrimethamine.

Chemoresistance of Plasmodium falciparum in the urban region of Yaounde, Cameroon. Part 2: Evaluation of the efficacy of amodiaquine and sulfadoxine-pyrimethamine combination in the treatment of uncomplicated Plasmodium falciparum malaria in Yaounde, Cameroon

The spread of chloroquine resistance or its stabilization at a high level calls for a change in the therapeutic strategy, including a possible replacement of chloroquine. We assessed and compared the efficacy of amodiaquine and sulfadoxine-pyrimethamine in Yaoundé. Of 140 adults and children > 5 years enrolled in the study, 59 in the amodiaquine and 58 in the sulfadoxine-pyrimethamine treatment group were followed until day 14. The efficacy of amodiaquine was 100%, whereas 12.1% of the patients treated with sulfadoxine-pyrimethamine responded with an early treatment failure. Side effects in both treatment groups were mild and did not require any specific treatment. We did in vitro drug assays for monodesethylamodiaquine (active metabolite of amodiaquine) and pyrimethamine and measured plasma levels of monodesethylamodiaquine, sulfadoxine, and pyrimethamine. Unlike amodiaquine, the results of the in vitro drug sensitivity test for pyrimethamine were not concordant with the clinical response. A wide inter-individual variation in the plasma drug levels was observed. Unlike chloroquine, the mean plasma concentrations did not vary with age. There was no significant difference in the plasma concentrations of sulfadoxine and pyrimethamine between patients responding with an adequate clinical response and those responding with treatment failure. Amodiaquine has several advantages over sulfadoxine-pyrimethamine combination and may be considered to be an effective drug in an endemic zone with a moderate level of chloroquine resistance.

Anti-malarial drug use among preschool children in an area of seasonal malaria transmission in Kenya

The aims of this study were to estimate the proportion of asymptomatic Kenyan preschool children using anti-malarial drugs, to identify factors associated with chloroquine use, and to assess the validity of frequency of febrile episodes and drug use reported by mothers or carers. Of 318 children studied, 38% (95% confidence interval [CI] = 30-47%]) tested positive for chloroquine or sulfadoxine. Of chloroquine-positive children, 15% had concentrations exceeding the estimated minimum therapeutically effective values. Among those testing negative for sulfadoxine, chloroquine-positive children were more frequently parasitemic (odds ratio = 2.6, 95% CI = 1.3-5.2), and had lower mean hemoglobin concentrations (6.1 g/L, 95% CI = 2.1-10.1) than chloroquine-negative children. Mothers over-reported the frequency of malaria or fever episodes as usually defined in medical studies, and underreported anti-malarial drug use. We conclude that anti-malarials are frequently given for treatment of malaria or malaria-associated illness, rather than prophylactically or for symptoms unrelated to malaria. Questionnaire surveys cannot replace biochemical markers to obtain information on anti-malarial drug use.

Concentrations of sulfadoxine and trimethoprim in plasma, lymph fluids and some tissues 24 h after intramuscular administration to Angora goats

This study was carried out to determine the concentrations of sulfadoxine and trimethoprim in plasma, lymph, and some tissues in goats after administration of a single recommended therapeutic dose. Five healthy, adult Angora goats were used. The drug combination, containing 200 mg sulfadoxine and 40 mg trimethoprim per millilitre, was given as a single IM injection at the recommended dose level, 15 mg/kg body weight for sulfadoxine and 3 mg/kg body weight for trimethoprim. The goats were slaughtered 24 hours after drug administration and samples were taken from liver, bone marrow, pelvic limb muscles, hepatic, thoracic duct, and the pelvic limb lymph fluids for analysis of drug concentrations by HPLC. The concentrations of trimethoprim in bone marrow, liver, pelvic limb muscles, hepatic lymph, the pelvic limb lymph, and thoracic duct lymph were found to be 6, 5, 4, 2, 5 and 15 times higher than those of plasma, respectively. Although the sulfadoxine concentrations in bone marrow, pelvic limb muscles, and liver were 2, 3 and 2 times higher than the plasma concentrations, respectively, the sulfadoxine concentrations in hepatic lymph, the pelvic limb lymph, and thoracic duct lymph were lower than those of plasma. The results show that the trimethoprim concentrations in lymph fluids were quite similar to those in tissues. However, the sulfadoxine concentrations in lymph fluids were different in each tissue.

The effect of sulfaphenazole and sulfadoxine on tolbutamide disposition in dwarf goats (Caprus hircus aegagrus)

The aim of the present study was to investigate the effects of intravenously administered sulfadoxine (5 mg kg-1 bodyweight) or sulfaphenazole (5 mg kg-1 bodyweight) on the in vivo elimination of i.v. tolbutamide (5 mg kg-1 bodyweight), as both compounds were shown to inhibit tolbutamide hydroxylation in vitro. It was shown that relative large differences in tolbutamide clearance exist among goats (n = 6). A high correlation was seen between tolbutamide and sulfadoxine clearances. Tolbutamide clearance was significantly reduced by concommitant administration of sulfaphenazole. Sulfadoxine (SDX) had a less consistent effect. Mean tolbutamide plasma clearance was not significantly affected due to the fact that three animals showed an inhibition, whereas three others apparently did not respond. A negative correlation was found between the amount of N4-acetyl SDX in urine and the SDX clearance. Approximately 93 per cent of tolbutamide was bound to plasma proteins. However, there was no evidence for displacement of tolbutamide from its protein binding sites by sulfaphenazole or sulfadoxine. The results described in the present study confirm previous in vitro data obtained with goat hepatocytes. Although quantitative differences in inhibition exist between in vivo and in vitro results, hepatocytes are a good model to study potential drug-drug interactions at the level of biotransformation processes.

Simultaneous determination of pyrimethamine and sulphadoxine in human plasma by high-performance liquid chromatography after automated liquid-solid extraction

A high-performance liquid chromatographic method with ultraviolet detection is described for the simultaneous measurement of pyrimethamine and sulphadoxine in human plasma. After an automated liquid-solid extraction on a C8 cartridge, the compounds are separated on a C18 column by isocratic elution; the mobile phase is methanol-acetonitrile-water (10:25:65, v/v/v) with triethylamine (1%) and adjusted to pH 5.6 with phosphoric acid. The eluent is monitored with an ultraviolet detector at 240 nm. The limit of quantification was 10 ng/ml for pyrimethamine and 22 microg/ml for sulphadoxine. No chromatographic interferences can be detected from endogenous compounds, other anti-malarial drugs or major drugs used for the treatment of children. Sulphadimethoxine is used as an internal standard. The method is accurate and precision is good with relative standard deviations lower than 6%. The chromatographic procedure takes 11 min. The method is comparatively rapid, simple, sensitive and can be used for therapeutic drug monitoring, clinical and pharmacokinetic studies.

Determination of trimethoprim and sulphadoxine residues in porcine tissues and plasma

Healthy gilts and market-ready hogs were administered a single intramuscular (IM) injection of Borgal, a commercial formulation of trimethoprim-sulfadoxine (TMP-SDX), once or twice daily. The objectives were to determine if a newly-developed high-performance liquid chromatographic (HPLC) method would be suitable for measuring the residual concentrations of TMP in the plasma of these live animals, and to determine if the administration of this veterinary drug would leave measurable residues in their plasma and tissues at slaughter. Plasma and tissue concentrations of SDX and TMP from these animals were determined over a period of 14 d using thin-layer chromatography/densitometry (TLCD), and the newly-developed HPLC method, respectively. The lowest detectable limit (LDL) for SDX in plasma and tissue was 20 ppb by TLCD. The HPLC method had a LDL of 5 ppb for TMP in plasma and tissue. Both methods were then used to provide baseline data on the absorption and depletion of TMP and SDX from these healthy animals. It was observed that both TMP and SDX were readily absorbed into the blood and tissues, but TMP was eliminated much faster than SDX. No TMP residues were detected in the plasma of any of the gilts at and beyond 21 h after drug administration. Also, no TMP residues were detected in the plasma of any of the market-ready hogs 24 h after drug administration at either the label dose or twice the label dose. Sulfadoxine residues at concentrations above the maximum residue limit (MRL) of 100 ppb were, however, detected in the plasma, muscle, kidney, liver, and injection sites of hogs slaughtered 1 and 3 d after a single IM administration at the label dose. Although SDX residues were still detectable in the lungs, kidney, liver and plasma of some hogs 10 d after administration of the label dose and twice the label dose, these were below the MRL. Postmortem examination revealed necrosis and inflammation at the injection sites, but no visible deposits of the injected drug.

High-performance liquid chromatography determination of pyrimethamine, dapsone, monoacetyldapsone, sulfadoxine, and N-acetyl-sulfadoxine after rapid solid-phase extraction

A solid-phase extraction procedure and a corresponding high-performance liquid chromatographic technique based on methods previously published by Edstein et al. (Edstein M. Quantification of antimalarial drugs. I. Simultaneous measurement of sulphadoxine, N4acetylsulphadoxine and pyrimethamine in human plasma. J Chromatogr 1984;305:502-7; Edstein M. Quantification of antimalarial drugs. II. Simultaneous measurement of dapsone, monoacetyldapsone and pyrimethamine in human plasma. J Chromatogr 1984;307:426-31) were developed for simultaneous determination of either dapsone (DDS), monoacetyldapsone (MADDS), and pyrimethamine (PYR) or sulfadoxine (SDX), N-acetyl-sulfadoxine (NAS) and pyrimethamine in plasma. Solid-phase extraction was achieved using C-18 extraction columns. An ionpair chromatography was performed on a C-18 analytical column (mu Bondapak C-18, 300 x 3.9 mm I.D.). Gradient elution with methanol, acetonitrile, PIC B6 reagent (1-hexanesulphonic acid), and water as mobile phase was applied. Ultraviolet detection was done at 210 nm for PYR, at 254 nm for SDX and NAS, and at 295 nm for DDS and MADDS. The extraction recoveries averaged 92.1% for PYR, 87.6% for DDS, 87.5% for MADDS, 91.2% for SDX, and 92.4% for NAS. The limit of quantification using 1.0-ml plasma samples was 15 ng/ml for PYR, DDS, MADDS, NAS, and 25 ng/ml for SDX (precision < 15%).

Plasmodium falciparum: increased proportion of severe resistance (RII and RIII) to chloroquine and high rate of resistance to sulfadoxine-pyrimethamine in Peninsular Malaysia after two decades

Uncomplicated falciparum malaria patients were randomly assigned to receive either 25 mg/kg chloroquine (CHL) over 3 d or a statim dose of 25 mg/kg sulfadoxine (SDX) plus 1.25 mg/kg pyrimethamine (PYR). Patients were followed up for 28 d and the parasite response graded according to World Health Organization criteria. Overall resistance to CHL was 63.3% and 47.4% to SDX/PYR. RI, RII and RIII rates were 9.1%, 42.4% and 12.1% for CHL and 10.5%, 21.1% and 15.8% for SDX/PYR, respectively. Degree and rates of resistance to CHL were significantly correlated with pre-treatment parasite density, but not those to SDX/PYR. Plasma CHL and SDX/PYR levels were within the reported ranges and were not significantly different in patients with sensitive and resistant responses.

Determination of sulfadoxine concentrations in whole blood using C18 solid-phase extraction, sodium dodecyl sulfate and dimethylaminocinnamaldehyde

A simple method is described for the extraction and subsequent analysis of sulfadoxine in human whole blood using a solid-phase extraction technique and colorimetric reaction. This procedure utilizes the micellar properties of sodium dodecyl sulfate to: (1) extract sulfadoxine from a C18 solid-phase sample-preparation column; (2) enhance the colorimetric reaction produced by the addition of p-dimethylaminocinnamaldehyde (DMAC); and (3) provide stability to the coloured product generated by the reaction of sulfadoxine with DMAC. The intense, violet-red colour reaction can be conveniently used for qualitative and semiquantitative visual interpretations of sulfadoxine levels. Under the assay conditions, drug concentrations in the blood of subjects receiving sulfadoxine were determined from absorbance measurements. These results correlated well with the sulfadoxine levels determined from high-performance liquid chromatographic analysis. Important advantages of the procedure include the ability to evaluate small samples of whole blood (100 microliters), the minimal use of organic solvents, no sophisticated instrumentation, and formation of a stable, coloured reaction product. The method proved to be a suitable field assay for determining whole-blood levels of sulfonamides in the concentration range from 5 to 100 micrograms ml-1.

[Demonstration of two trimethoprim/sulfonamide combinations in bronchoalveolar lavage fluid of horses and determination of blood levels]

Five healthy horses were given a sulfadoxine/trimethoprim combination (Borgal, Hoechst AG) i.v. on day 1. The next ten days the horses got once a day a sulfadimethoxine/trimethoprim combination orally (Trafigal, Hoechst AG). The doses were given as recommended. One horse received no medicaments for control. On each horse six bronchoalveolar lavages were performed. Blood samples were taken to calculate blood levels and elimination half lives. To determine the amount of substances in lavage fluid and plasma the high performance liquid chromatography (HPLC) was used. Regularly low quantities of sulfonamides and trimethoprim were detected in lavage-samples. The mean plasma concentration (n = 4) of sulfadoxine and trimethoprim 30 min after i.v. administration was 71.6 and 1.13 micrograms/g respectively. 24 h after injection the sulfadoxine blood level was 3.0 micrograms/g, while trimethoprim was no longer detectable. The average elimination half lives of sulfadoxine and trimethoprim were 7.94 h and 1.35 h respectively. 8 h after oral application (n = 5) the highest mean sulfadimethoxine blood levels of 53.8 micrograms/g were measured. The elimination half life of sulfadimethoxine was 9.77 h. Two hours after feeding the drug the first blood samples were taken. They already contained the highest mean trimethoprim concentration of 0.32 microgram/g plasma.

High-performance liquid chromatography determination of dapsone, monoacetyldapsone, and pyrimethamine in filter paper blood spots

A high-performance liquid chromatography method for the simultaneous analysis of dapsone (DDS), the major metabolite of DDS, monoacetyldapsone (MADDS), and pyrimethamine (PYR) was modified for capillary blood samples obtained by finger prick and dried on filter paper. Limit of quantitation using 150 microliters whole blood dried on filter paper was found to be 20 ng/ml for DDS and PYR and 15 ng/ml for MADDS (precision < 15%). The clinically relevant concentrations of DDS are 50-2,000 ng/ml and for PYR 25-150 ng/ml. No interference from several drugs were observed. The accuracy of the filter paper method and the original whole-blood method was almost comparable. Standardization could therefore be obtained by the more simple whole-blood method. Dried filter paper samples stored at 19-22 degrees C were stable for months and for 2 weeks stored at 35 degrees C. The concentrations of simultaneously collected capillary blood and conventional venous blood samples correlated well. The present method using capillary blood dried on filter paper is reliable, simple, sensitive, and applicable in the field with limited technical facilities.

Sulphadoxine concentrations in plasma, red blood cells and whole blood in healthy and Plasmodium falciparum malaria cases after treatment with Fansidar using high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method using acetonitrile-methanol-(1M) perchloric acid-water (30:9:0.8:95, v/v/v/v) at a flow of 1.5 ml min-1 on mu-Bondapak C18 column with UV (254 nm) detection has been developed for the separation of sulphadoxine, sulphalene and sulphamethoxazole from other antimalarials. Calibration curves were linear in the range 0.5-100 micrograms ml-1. The limit of quantitation was 50 ng ml-1. Within-day and day-to-day coefficients of variation averaged 2.1 and 6.45%, respectively. The extraction recovery of sulphadoxine from plasma, red blood cells and whole blood was 90.28, 92.05 and 94.69%, respectively. The method has been used for the determination of sulphadoxine concentrations in plasma, red blood cells and whole blood of eight healthy and 50 Plasmodium falciparum malaria cases after administration of two tablets of Fansidar. Mean sulphadoxine concentration in plasma was higher than red blood cells or whole blood. Sulphadoxine concentration in plasma and whole blood of P. falciparum malaria cases was significantly higher as compared to healthy volunteers while it was the same in red blood cells. Sulphadoxine was absorbed much less in red blood cells than in plasma or whole blood.

A study of the comparative bioavailability of pyrimethamine-sulfadoxine obtained from two oral preparations

The bioavailability of two oral preparations of pyrimethamine-sulfadoxine are compared in a randomised cross-over study. Pyrimethamine(PM)-sulfadoxine(SD) was given orally in a single dose to healthy male adults (SD 12 mgkg-1; PM 0.64 mgkg-1). For Fansidar(Hoffman-LaRoche) the mean AUC for PM and SD were; 0.47 mghl-1 and 45.4 mghl-1, and for Falcidin(Cosmos), the mean AUC for PM and SD were; 0.49 mg hl-1 and 42.9 mghl-1 respectively. There was no significant difference in bioavailability of PM or SD between the two preparations.

Pharmacokinetics of sulphadoxine and trimethoprim in sows: influence of lactation

A potentiated sulpha drug was administered intravenously to 12 sows on the 17th day of lactation and to 4 sows in early pregnancy to study the influence of lactation on its disposition kinetics. The dose-rate of sulphadoxine (SDX) used was 12 mg/kg b.w. while that of trimethoprim (TMP) was 2.4 mg/kg b.w. The pharmacokinetic parameters of SDX showed no significant difference between lactating and pregnant sows (Vss, 0.24 +/- 0.04 L/kg; Cls, 0.25 +/- 0.05 ml/min per kg: MRT, 17.08 +/- 4.48 h). SDX did not accumulate in milk, the concentrations in milk being less than the concentrations in serum at the same time. Of the pharmacokinetic parameters for TMP, only the mean residence time was significantly different between the two groups (Vss, 1.60 +/- 0.31 L/kg; Cls, 4.62 +/- 1.07 ml/min per kg: MRTlactating, 5.43 +/- 1.26 h; MRTpregnant, 7.74 +/- 1.72 h). TMP was excreted in milk to a considerable extent, the ratio of its concentration in milk to that in serum at the same time being over 2.2. These two substances show a completely different pharmacokinetic behaviour. Even though TMP is excreted more quickly in lactating sows, adjusting the dose of this potentiated sulpha drug does not seem to be appropriate.

Mefloquine level monitoring in patients with multidrug resistant Plasmodium falciparum on the Thai Myanmar border

A total of 42 patients with uncomplicated falciparum malaria who attended the malaria clinic in Mae Sot, Tak Province were treated with single oral dose of MSP 3 tablets (Fansimef, equivalent to 750 mg of mefloquine) concurrently with primaquine (30 mg). They all contracted the infection from Cambodia. The aim of the study was to monitor the efficacy of MSP 3 tablets for the treatment of this highly multiple drug resistant strains of Plasmodium falciparum in this area. Of the 39 patients included for efficacy assessment, 13 (33.3%) patients had sensitive responses, whereas 15 (38.5%) and 8 (20.5%) had RI and RII types of response, respectively. Melfoquine concentrations on Day-3 after treatment in patients with sensitive and treatment failure groups were comparable; the respective mean (SD) values were 665 (279) and 772 (264) ng/ml.

A single dose of intramuscular sulfadoxine-pyrimethamine as an adjunct to quinine in the treatment of severe malaria: pharmacokinetics and efficacy

It has been suggested that sulfadoxine-pyrimethamine (SD/PM) may be useful in the treatment of severe malaria since it could enhance the killing of parasites by quinine (QN) and it can be given as a single intramuscular injection. Eighty Kenyan children with severe malaria were allocated at random to receive either intramuscular QN alone (quinine dihydrochloride 20 mg salt/kg as a loading dose, followed by 10 mg salt/kg 12 hourly for a total of 6 doses) or the same QN regimen plus one intramuscular injection of SD/PM (sulfadoxine 25 mg/kg, pyrimethamine 1.25 mg/kg). There was no difference in time to defervescence, aparasitaemia, or 50% reduction in parasitaemia, parasite elimination half-life, or mortality between the 2 groups. In addition, the concentrations of SD and PM were measured in 14 children and of QN in 8 of these children. Concentrations needed to achieve synergy against PM-resistant strains of Plasmodium falciparum were achieved in all of the children with severe malaria within the first hour and maintained for more than 72 h. SD/PM did not perturb the pharmacokinetics of QN.

The disposition of oral and intramuscular pyrimethamine/sulphadoxine in Kenyan children with high parasitaemia but clinically non-severe falciparum malaria

1. H.p.l.c. methods are described for the measurement of pyrimethamine and sulphadoxine in small volumes of plasma dried on filter paper strips. 2. Pyrimethamine/sulphadoxine (Fansidar, Hoffman LaRoche) was given by mouth and by intramuscular injection to children with uncomplicated falciparum malaria but with high parasitaemia (n = 8 for both routes; pyrimethamine 1.25 mg kg-1, sulphadoxine 25 mg kg-1). 3. Plasma concentrations of pyrimethamine and sulphadoxine associated with synergistic effects against pyrimethamine-resistant strains of Plasmodium falciparum in vitro were achieved within 1 h of administration and were maintained beyond the end of sampling. 4. After both oral and parenteral administration the plasma concentrations of both compounds were lower than those predicted by data from healthy subjects. 5. Areas under the plasma concentration-time curves of sulphadoxine after oral and i.m. administration did not differ significantly, although maximum plasma drug concentrations were higher after the i.m. route (P = 0.03). 6. The AUC values of pyrimethamine did not differ significantly between the two routes of administration. However, after i.m. administration AUC(0,24 h) values were smaller (P = 0.03), and the time to maximum plasma drug concentration (tmax) was longer (P = 0.004) than when the drug was given orally.

Reversed-phase liquid chromatographic method for the simultaneous determination of the antimalarial drugs sulfadoxine, pyrimethamine, mefloquine and its major carboxylic metabolite in plasma

A high-performance liquid chromatographic (HPLC) method for the simultaneous determination of sulfadoxine, pyrimethamine, mefloquine and the carboxylic metabolite of mefloquine in plasma is described. After the proteins have been precipitated with a combination of zinc sulphate and acetonitrile containing two internal standards, pyrimethamine and mefloquine are extracted as bases and sulfadoxine and the carboxylic metabolite of mefloquine as ion-pairs with tetrabutylammonium. The drugs are separated by HPLC on a 3 micron octadecylsilica column with ultraviolet detection at 229 nm. The method is simple and reliable and enables the simultaneous determination of the drugs in 600-microliter plasma samples with a sensitivity suitable for standard drug monitoring purposes.

Isoniazid acetylating phenotype in patients with paracoccidioidomycosis and its relationship with serum sulfadoxin levels, glucose-6-phosphate dehydrogenase and glutathione reductase activities

The authors evaluated the isoniazid acetylating phenotype and measured hematocrit, hemoglobin, glucose-6-phosphate dehydrogenase and glutathione reductase activities plus serum sulfadoxin levels in 39 patients with paracoccidioidomycosis (33 males and 6 females) aged 17 to 58 years. Twenty one (53.84%) of the patients presented a slow acetylating phenotype and 18(46.16%) a fast acetylating phenotype. Glucose-6-phosphate-dehydrogenase (G6PD) activity was decreased in 5(23.80%) slow acetylators and in 4(22.22%) fast acetylators. Glutathione reductase activity was decreased in 14(66.66%) slow acetylators and in 12(66.66%) fast acetylators. Serum levels of free and total sulfadoxin were higher in slow acetylator (p less than 0.02). Analysis of the results permitted us to conclude that serum sulfadoxin levels are related to the acetylator phenotype. Furthermore, sulfadoxin levels were always above 50 micrograms/ml, a value considered therapeutic. Glutathione reductase deficiency observed in 66% of patients may be related to the intestinal malabsorption of nutrients, among them riboflavin, a FAD precursor vitamin, in patients with paracoceidioidomycosis.

Quantitation of Fansimef components (mefloquine + sulfadoxine + pyrimethamine) in human plasma by two high-performance liquid chromatographic methods

Two simple, precise, and selective high-performance liquid chromatographic methods are described for the simultaneous quantitation of mefloquine (MQ) plus pyrimethamine (PYR) or sulfadoxine (SDX) plus its principal metabolite N4-acetylsulfadoxine (N4SDX) in human plasma. After a single-step extraction, MQ plus PYR and SDX plus N4SDX including internal standards were separated using ion-paired and ion-suppression chromatography. Total run times for the assays were less than 12 min. Intraassay and interassay precision of the methods expressed as the coefficients of variation were less than 9% in plasma for the four compounds. The extraction recovery averaged 98% for MQ, 97% for PYR, 96% for SDX, and 81% for N4SDX. Plasma concentrations of the four compounds in a pediatric patient after a single oral dose of Fansimef (MQ + SDX + PYR) were determined to demonstrate the clinical application of the methods.

Standard and reduced doses of sulfadoxine-pyrimethamine for treatment of Plasmodium falciparum in Tanzania, with determination of drug concentrations and susceptibility in vitro

88 asymptomatic Tanzanian schoolchildren with Plasmodium falciparum parasitaemia were given all, half or quarter of the recommended standard therapeutic dose of sulfadoxine-pyrimethamine (Fansidar). All children cleared the parasites by day 3 and all remained negative during 28-42 days of follow-up. All 32 successful in vitro micro-tests showed full sensitivity. High performance liquid chromatographic methods were applied for drug determinations. Using 100 microliter capillary blood dried on filter paper for sulfadoxine determination the inter-individual variation during follow-up of the standard dose group was 2-4 fold and the median half life was 8.9 d. Sulfadoxine concentrations in the half and quarter dose groups were roughly proportional to those in the standard dose group. The median whole blood to plasma concentration ratio for sulfadoxine was 0.72 and the correlation coefficient 0.95. There was only a weak correlation (r=0.46) between plasma concentrations of sulfadoxine and pyrimethamine. The uniform efficacy of sulfadoxine-pyrimethamine in vivo, even when reduced doses were used, makes this combination a good alternative for treatment of P. falciparum in Tanzania.

Pharmacokinetics of the combination pyrimethamine with sulfadoxine and mefloquine (FANSIMEF) in Chinese volunteers and the relative bioavailability of a lacquered tablet

The oral single-dose pharmacokinetics and bioavailability of mefloquine (M) in combination with pyrimethamine (P) and sulfadoxine (S) from a single non-lacquered tablet (NL; M 250 mg, P 25 mg, S 500 mg) and two lacquered tablets (L; M 125 mg, P 12.5 mg, S 250 mg) were investigated in 6 healthy Chinese volunteers. The plasma concentrations of P and S were measured by high-performance liquid chromatography with UV detector over 11 days and the plasma concentrations of M were measured by gas chromatography with electron capture for 63 days. The pharmacokinetic evaluation of each of the three components was based on the assumption of an open linear one-compartment model. The model-independent pharmacokinetic parameters such as elimination half-life and total clearance of P and S in the present study were not appreciably different from those reported previously. The pharmacokinetic parameters of elimination half-life, total clearance and apparent volume of distribution of M were 11 days, 45.8 ml/h.kg, and 14.8 l/kg, respectively. Compared to previously published data on M in Thai patients, Caucasian, Brazilian and African subjects, it was found that the elimination half-life in Chinese subjects was similar to that in Thai patients, but different from Caucasian, Brazilian and African subjects. There were significant differences in total clearance and volume of distribution among Chinese subjects and Thai patients. The differences in pharmacokinetic behaviour of M between subject groups needs to be examined further. The relative bioavailability of P, S, and M in the lacquered and non-lacquered tablet formulations in the 6 subjects studied were not significantly different with values (mean +/- SD) of 0.98 +/- 0.06, 1.28 +/- 0.20 and 1.02 +/- 0.17, respectively.

Chemosuppression of malaria by the triple combination mefloquine/sulfadoxine/pyrimethamine: a field trial in an endemic area in Malaysia

Malaria, particularly that due to chloroquine-resistant Plasmodium falciparum, which requires management with antimalarial drugs capable of protecting against multiresistant strains, has emerged in Malaysia. A study was carried out to assess the efficacy and tolerability of 2 dosages of mefloquine/sulfadoxine/pyrimethamine (MSP; RO 13-5112) compared to Fansidar in a malaria endemic area. 914 subjects in 3 random groups were studied. Occurrence of malaria was assessed both clinically as well as by blood films. Plasma drug levels were also measured. The results showed that the low dose of MSP was completely effective in suppressing parasitaemia. 2.7% of the study population reported adverse drug reactions, the lowest incidence being in subjects on the low dose; their blood chemical profiles were also the least affected. The plasma levels of pyrimethamine and sulfadoxine achieved in the low dose group were slightly higher than expected, but there was no significant difference in bioavailability. The study showed that, for chemoprophylaxis, a low dose of MSP provided effective protection with minimal side effects.

Plasma concentrations of sulfadoxine in healthy and malaria infected Thai subjects

The disposition of sulfadoxine was studied in the presence of pyrimethamine in 18 healthy Thai subjects who had been suffering from falciparum malaria in the 6 months prior to the study, and in 12 Thai patients with acute malaria. The volunteers were administered an oral dose of 500 mg sulfadoxine + 25 mg pyrimethamine (1 Fansidar tablet). They were classified retrospectively as responders (Group I, n = 8) or nonresponders (Group II, n = 10) according to previous response to treatment with Fansidar. The patients were treated with 3 Fansidar tablets corresponding to 1500 mg sulfadoxine and 75 mg pyrimethamine. Five of them were completely cured. Seven patients showed R I or R II resistance. In all cases blood samples were collected up to 288 h post dose. The resultant plasma was analyzed for active (i.e. unchanged) and total sulfadoxine using a modified Bratton-Marshall method. In the healthy volunteers the plasma concentration time course of total sulfadoxine was similar for responding and nonresponding subjects. However, in nonresponders active sulfadoxine tended to show shorter half-lives (harmonic means were 212 h vs 267 h, respectively). Furthermore, significantly higher amounts of metabolites (mainly N4-acetylsulfadoxine) were present in plasma of nonresponders. In contrast to these findings, in malaria patients, plasma concentrations of active and total sulfadoxine were even higher in nonresponders as compared to the subjects who could be successfully cured. Furthermore, in this case there was no increase of the amount of metabolites in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfadoxine assay using capillary blood samples dried on filter paper--suitable for monitoring of blood concentrations in the field

A high performance liquid chromatographic method for determination of sulfadoxine in whole blood obtained by finger prick and dried on filter paper is presented. The technique was validated by comparing the sulfadoxine concentration of simultaneously collected capillary blood dried on filter paper and conventional venous whole blood samples. Agreement between capillary blood dried on filter paper and venous whole blood was satisfactory. Limit of determination using 100 microliter of capillary blood was found to be 25 mumol/L (7.8 micrograms/ml). Sulfadoxine was stable in the dried filter papers for at least 15 weeks at +37 degrees C. The concentration ratio between plasma and whole blood of sulfadoxine was found to be approximately 1.8. The sampling technique on filter paper offers a convenient method for overcoming many of the practical problems of blood sampling in the field.

Pharmacokinetics of sulfadoxine and pyrimethamine after Fansidar administration in man

The pharmacokinetics of sulfadoxine (SULF) and pyrimethamine (PYR) were studied in 7 healthy volunteers after a single oral dose of Fansidar. A comparison was made between the pharmacokinetics of the components of Fansidar calculated from whole blood and plasma data. The mean whole blood to plasma concentration ratios of SULF and PYR were 0.62 and 0.87, respectively. The elimination half-lives of SULF and PYR were similar in whole blood and plasma. The apparent volume of distribution and clearance of SULF and PYR in whole blood were significantly higher (p less than 0.01) than the corresponding plasma values. Because malaria-infected erythrocytes appear to concentrate SULF, it may be more relevant to measure drug concentrations in whole blood rather than in plasma in assessing the antimalarial efficacy of Fansidar.

Multiple-dose pharmacokinetics of the antimalarial drug Fansimef (pyrimethamine + sulfadoxine + mefloquine) in healthy subjects

Fansimef is a new antimalarial combination containing pyrimethamine, sulfadoxine and mefloquine in the weight proportions 1 + 20 + 10. It has been designed to fight plasmodia resistant to the presently used antimalarial drugs and to counter the development of new resistant forms of the parasites. In the present study tablets containing 25 mg pyrimethamine, 500 mg sulfadoxine and 250 mg mefloquine were used. Six Brazilian volunteers received a loading dose of 2 tablets followed by 20 maintenance doses of 1 tablet at a dosage interval of 7 days. The pharmacokinetic evaluation of each of the three components was based on the assumption of an open linear two-compartment model. After the last maintenance dose the following kinetic parameters were determined for pyrimethamine, sulfadoxine and mefloquine, respectively: elimination half-life = 123, 179 and 550 h; volume of distribution in the postdistributive phase = 2.5, 0.15 and 18.6 1 X kg-1, and total systemic clearance = 14.0, 0.64 and 24.0 ml X h-1 X kg-1. All these values agree fairly well with those measured in previous single-dose kinetic studies. At steady state, Cmin values of each of the three components generally showed small variations. No unexpected accumulation of any of the three components was observed, indicating that induction or inhibition of metabolic enzymes did not occur during the trial.

Simultaneous determination of pyrimethamine and sulphadoxine in human plasma by high-performance liquid chromatography

Pyrimethamine was extracted as a base, and sulphadoxine simultaneous as an ion pair with tetrabutyl-ammonium into methylene chloride. After re-extraction into an acidic aqueous phase separation of the drugs was performed by reversed-phase high performance liquid chromatography using Nucleosil C-18 as the support and acetonitrile-phosphate buffer pH 5.5 (28 + 72) as the mobile phase with tetrabutyl-ammonium as counter ion. Photometric detection at 240 nm was used for both substances. The within-day precision of the method was 5 to 10% for pyrimethamine within 50 to 1000 nmol/l (13 to 250 ng/ml) and for sulphadoxine 3 to 6% within 50 to 1000 mumol/l (16 to 310 micrograms/ml) in plasma. The method is suitable for simultaneous determination of plasma levels of pyrimethamine and sulphadoxine after therapeutic doses of Fansidar.

High-performance liquid chromatographic assay of pyrimethamine, sulfadoxine and its N4-acetyl metabolite in serum and urine after ingestion of Suldox

A sensitive and selective reversed-phase high-performance liquid chromatographic assay has been developed to determine the concentration of pyrimethamine, sulfadoxine and N4-acetylsulfadoxine in serum and urine after oral administration of the antimalarial remedy Suldox. Hitherto the literature describes no method being able to quantitate all three compounds in these fluids. The compounds are extracted successively from the same sample and subjected to liquid chromatography followed by ultraviolet detection (280 nm). Calibration curves were linear (r2 = 0.999; S.E.M. less than 3%; n = 10) in the range 0-300 micrograms/ml (sulfadoxine) and 0-1000 ng/ml (N4-acetylsulfadoxine and pyrimethamine). The limits of quantitation for the latter compounds were as low as about 5 ng/ml and 1 ng/ml, respectively. At therapeutic serum concentrations of 30 micrograms/ml (sulfadoxine), 350 ng/ml (N4-acetylsulfadoxine) and 120 ng/ml (pyrimethamine) an interassay reproducibility below 8% (relative standard deviation) was found for all three compounds. The assay was evaluated in a pilot study and proved convenient for pharmacokinetic studies in man following oral co-administration of pyrimethamine and sulfadoxine.

Plasma concentrations in pyrimethamine and sulfadoxine and evaluation of pharmacokinetic data by computerized curve fitting

For the determination of the plasma concentration profiles of pyrimethamine and sulfadoxine after the administration of 1 tablet of Fansidar, highly specific analytical methods are needed as the pyrimethamine concentration is low (0.2 - 0.02 mg/litre) and the concentration ratio of the two components in the plasma is high (> 1: 500). The microbiological method described in this paper fulfils these requirements for high specificity and sensitivity (the sensitivity limit for sulfadoxine is 1 mg/litre and for pyrimethamine is 0.013 mg/litre).Pharmacokinetic data were evaluated for 14 volunteers after administration of 1 tablet of Fansidar, and a computer simulation of multiple dosing (1 tablet per week) was performed.

Highly sensitive and specific determination of mefloquine in biological fluids using gas chromatography mass spectrometry with selected ion monitoring

A highly sensitive and specific assay for the determination of racemic erythro-alpha-(2-piperidyl)-2,8-bis(trifluoro-methyl)-4-quinoline-methanol in whole blood, plasma and urine has been developed. The method involves the extraction of the drug together with an internal standard, formation of the corresponding O-trimethylsilyl-N-trifluoroacetyl derivatives, gas chromatographic separation and mass spectrometric measurement of the peaks by selected ion monitoring. The method has a sensitivity of 1 ng ml-1 for plasma and 3 ng ml-1 for whole blood or urine. It has been applied to the analysis of mefloquine in plasma following an oral dose of 250 mg of the drug to healthy subjects. No interference was observed from the simultaneous administration of Fansidar.